Several lines of evidence suggest that several amino acids may serve as synaptic transmitters in mammalian central nervous system. At present, supporting evidence for such a role is best for gamma aminobutyric acid (GABA) and glycine. However, unlike known neurotransmitters, GABA and glycine participate in other pathways of cellular metabolism. Thus, if amino acids serve as transmitters, one would expect at least two functional pools, one of which is the transmitter pool. Little is known about the compartmentation of these amino acids and the nature and location of the postulated transmitter pool. This project proposes to examine the nature and location of the GABA pools in brain slices, synaptosomes, and glial and neuronal enriched cell fractions. An in vitro superfusion system will be used to examine the release of endogenous and preloaded labeled amino acids from these preparations in response to electrical field stimulation, high potassium solutions, and carrier mediated exchange diffusion. The effect of various drugs on the release of GABA produced by these means will also be examined.